U.S. patent number 4,447,364 [Application Number 06/461,467] was granted by the patent office on 1984-05-08 for method for the preparation of liquid aluminum citrate.
This patent grant is currently assigned to Miles Laboratories, Inc.. Invention is credited to Philip W. Staal.
United States Patent |
4,447,364 |
Staal |
May 8, 1984 |
Method for the preparation of liquid aluminum citrate
Abstract
Disclosed is a method for the preparation of a stable solution
of aluminum citrate. The method involves combining a solution of
aluminum chloride with a solution of citric acid while maintaining
vigorous agitation. After formation of the aluminum citrate
solution, sufficient alkali metal or ammonium hydroxide is added to
increase the pH to a level of 5.5 to 7.5. During addition of the
base, the agitation is continued and the temperature of the
solution is maintained at a level of from 20.degree. C. to
90.degree. C.
Inventors: |
Staal; Philip W. (Elkhart,
IN) |
Assignee: |
Miles Laboratories, Inc.
(Elkhart, IN)
|
Family
ID: |
26850843 |
Appl.
No.: |
06/461,467 |
Filed: |
January 27, 1983 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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295227 |
Aug 21, 1981 |
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153766 |
May 27, 1980 |
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Current U.S.
Class: |
556/175;
556/183 |
Current CPC
Class: |
C07C
51/412 (20130101); C07C 51/412 (20130101); C07C
59/265 (20130101) |
Current International
Class: |
C07C
51/41 (20060101); C07D 103/04 (); C07F
005/06 () |
Field of
Search: |
;260/448B,448R |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
Other References
Chemical Abstracts, vol. 89, #199106e, Montedison, "Tanning", 1978.
.
Chemical Abstracts, vol. 83, #167105p, Kwong et al, "Influence of
Citric Acid on the Crystallization of Aluminum Hydroxide", 1975.
.
Chemical Abstracts, vol. 89, #164958q, Ancona et al., "Tanning
Agent for Skins", 1978..
|
Primary Examiner: Trousof; Natalie
Assistant Examiner: Covington; Raymond K.
Attorney, Agent or Firm: Jeffers; Jerome L.
Parent Case Text
BACKGROUND OF THE INVENTION
This application is a continuation-in-part of co-pending
application Ser. No. 295,227 filed Aug. 21, 1981 which is in turn a
continuation-in-part of application Ser. No. 153,766 filed May 27,
1980.
Claims
What is claimed is:
1. A method for the preparation of an aqueous solution of an
aluminum citrate complex which consists essentially of the
following steps:
(a) providing an aqueous solution of AlCl.sub.3 containing up to
about 34 weight % AlCl.sub.3 ;
(b) combining the AlCl.sub.3 solution with an aqueous solution of
citric acid containing up to about 50 weight % citric acid, while
vigorously agitating the resultant solution, to form an aluminum
citrate solution having a mole ratio of aluminum ion to citric acid
molecule of from about 1.5:1 to 2.0:1, said AlCl.sub.3 solution
being provided in an amount sufficient to form an aluminum citrate
solution containing from 1 up to about 3 weight % aluminum; and
(c) adding a basic hydroxide of the formula MOH where M is an
alkali metal or ammonium cation to the aluminum citrate solution,
while continuing to agitate the solution and while maintaining its
temperature within the range of from 20.degree. C. to 90.degree.
C., in sufficient quantity to raise the pH of the solution to a
level of from 5.5 to 7.5.
2. The method of claim 1 wherein the mole ratio of aluminum ion to
citric acid is about 1.9:1.
3. The method of claim 1 wherein the temperature is maintained at a
level of from 40.degree. C. to 60.degree. C. during the addition of
the basic hydroxide.
4. The method of claim 1 wherein the basic hydroxide is NaOH.
5. The method of claim 4 wherein the NaOH is added in the form of
its 50% (w/w) aqueous solution.
6. The method of claim 1 wherein sufficient basic hydroxide is
added to raise the pH to a level of from 6.0 to 7.0.
7. A method for the preparation of a stable liquid aluminum citrate
which consists essentially of the following steps:
(a) providing an aqueous solution of aluminum chloride containing
up to about 34% (w/w) of aluminum chloride;
(b) combining the aluminum chloride solution with an aqueous
solution of citric acid containing up to about 50% (w/w) citric
acid while providing vigorous agitation to form a solution of
aluminum citrate containing from 1 to about 3 weight % aluminum and
having a mole ratio of aluminum ion to citric acid molecule of from
about 1.5:1 to about 2:1; and
(c) adding a 50% (w/w) solution of sodium hydroxide to the aluminum
citrate solution, while continuing to provide vigorous agitation
and maintaining the temperature of the resultant at a level of from
40.degree. C. to 60.degree. C., to raise the pH to a level of from
6.0 to 7.0.
Description
The removal of oil from underground formations can be divided into
3 steps. The first step called primary recovery is to allow the oil
to flow out of the ground, relying on natural forces or using a
simple pumping technique to lift the oil to the surface. The life
span of primary recovery operations for a well can vary from only a
few years to 30 years or more, depending on the type of formation
involved, the viscosity of the crude, the gas content of the oil
and permeability of the reservoir. Under normal conditions, 5% to
25% of the oil in the formation is removed using primary recovery
leaving a significant portion of the oil to be removed by more
difficult and expensive techniques.
In some fields, the oil saturated formation is contiguous with a
larger, porous, water containing formation called an aquifer. If
this adjoining aquifer outcrops, it will have a continuous supply
of salt brine which will feed into the oil reservoir, providing a
constant drive to replace the oil removed. The result is as much as
30% of the oil being removed from the reservoir with the economic
limit being reached when the oil-water mixture is so high in water
that the oil produced does not pay for the pumping and separation
costs.
Unfortunately, not all formations are of the above type and
secondary recovery operations such as "water flooding" are
necessary. In this operation, injection wells are drilled at
intervals throughout the field and water is pumped into the
oil-bearing formation to displace the oil towards the producing
wells. This method has become very popular and results in average
total recovery, using both primary and secondary techniques, of 30%
to 33%.
The remaining oil, amounting to two thirds of the original volume,
is the target of tertiary recovery techniques called "Enhanced Oil
Recovery" or EOR. One of the first EOR techniques is steam flooding
of reservoirs which contain highly viscous crude which is difficult
or impossible to remove without raising its temperature to reduce
its viscosity. This can be accomplished by injection of high
pressure steam or causing underground combustion which results in
crude thin enough to be pumped to the surface. Another less popular
technique is to pump fluids that mix easily with the oil to the
producing well. Light hydrocarbons have been used in this technique
although liquefied CO.sub.2 has gained wider favor. In practice,
problems with efficiency and uniformity of the CO.sub.2 sweep
throughout the reservoir have retarded the widespread application
of this technique.
A third technique for EOR that is presently gaining acceptance in
the field is the use of chemicals and chemical processes to
increase oil production. When the reservoir undergoes a
water-flood, much of the oil remains behind attached to the walls
of the capillary passages and trapped in the pores of the sandstone
formation. The water-flood, always following the path of least
resistance, bypasses or slides past the oil. A reduction in surface
tension by the injection of chemicals can help break this oil loose
from the formation. Adding only a surfactant or micellar
dispersion, however, does not release much additional oil. After
such investigation, several systems were developed to push the
surfactant and oil through the formation in a uniform manner.
Polymers such as polyacrylamide, carboxymethylcellulose and
polysaccharides have been found to possess the desirable properties
needed to act as a fluid piston and drive the oil towards the
producer well. In practice, the micellar dispersion containing
surfactant is pumped into the formation followed by the polymer,
which is injected as a fairly linear, low-viscosity molecule in
order to permeate the microscopic pores of the sandstone. The
polymer is then thickened in the formation by introducing metal
ions such as aluminum complexed as aluminum citrate to cross-link
the polymer and form a gel. At this point, the gel is moved using
water flooding techniques resulting in a sweep of the oil bank
towards the producer well. This process is more fully described in
U.S. Pat. No. 3,762,476 issued Oct. 2, 1973.
A second system, similar to the micellar polymer flood but
different in its action, involves the injection of a cationic or
anionic polymer, depending on the electrical charge of the
sandstone in the formation, followed by aluminum citrate to
cross-link and gel the polymer. The polymer, by virtue of its ionic
charge, is attached to the capillary walls, thereby filling the
voids and larger bypass pores while avoiding the smallest passages.
The result is a more uniform pore size throughout the formation
which results in increased oil production during water
flooding.
Aluminum citrate is preferred for use as the cross-linking material
because of its low cost and the slow release of aluminum which
results in a relatively long period of activity after its injection
into the formation. In a typical operation, aluminum sulfate
hydrate (alum) and sodium citrate dihydrate are dry blended,
shipped to the well field, dispersed in water and pumped into the
formation. Water dispersion of the dry blend at the well site is
necessary due to the unavailability of a suitable method for the
preparation of a stable water solution of aluminum citrate. This
method suffers from several disadvantages. First of all, the solid
ingredients dissolve slowly and often incompletely in water and the
incompletely dissolved material can cause mechanical wear on seals
and moving parts of injection pumps. Furthermore, there is no
control over the pH of the solution which is corrosive at its
normal pH of about 2.5. In addition, the use of alum introduces
sulfate into the formation which when acted upon by sulfate
reducing bacteria, results in the presence of corrosive quantities
of H.sub.2 S.
British Patent Specification No. 1,598,709 discloses a tanning
material prepared by dissolving 2.8 kg of citric acid monohydrate
in 11 kg of H.sub.2 O and adding this solution to 33 kg of an
aqueous solution of AlCl.sub.3 and Al.sub.2 (SO.sub.4).sub.3
containing 11% Al as Al.sub.2 O.sub.3 at a pH of 1.7. This solution
is then adjusted to pH 4.1-4.2 by the addition of H.sub.2 SO.sub.4
and sufficient NaOH to raise the pH to the desired level. A
substantial amount of aluminum citrate prepared by this method
stays in solution at the pH of about 4 which is suitable for use in
the tanning industry but too acidic for use in enhanced oil
recovery. Increasing the pH to that which would be suitable for use
in an oil bearing formation is not satisfactory with this
composition, which has a ratio of aluminum ion to citric acid
molecule of 5.2:1.0, because at the higher pH most of the aluminum
citrate precipitates out of solution thereby rendering the solution
too dilute for commercially viable use in enhanced oil recovery.
Furthermore, the high ratio of aluminum to citrate in this
formulation results in the presence of unchelated aluminum which is
undesirable in the gelling system under consideration because its
presence causes rapid and uncontrolled cross-linking of the
polymer. The maximum ratio of fully chelated aluminum to citrate is
2:1.
Grossmith, et al disclose in U.S. Pat. No. 3,391,176 compounds of
the general formula:
where M is magnesium, calcium, sodium, potassium or ammonium and M'
is aluminum, magnesium, iron or calcium and AO is the salicylato
bidendate ion with Z being an integer of 1 to 4. The patentee's
stated purpose for preparing these double salts is to provide a
form of salylic acid which can be ingested without causing gastric
distress.
Goldsmith in U.S. Pat. No. 3,200,136 and Niedercorn in U.S. Pat.
No. 2,327,815 disclose the preparation of very dilute solutions of
aluminum citrate having a molar ratio of aluminum ion to citric
acid molecule of 1:1. Examples 5 of the '136 patent discloses a
solid aluminum citrate with a ratio of 2:1 which has a solution pH
of 3.
SUMMARY OF THE INVENTION
The present invention is a method for the preparation of an aqueous
solution of an aluminum citrate complex which comprises the steps
of:
(a) providing an aqueous solution of AlCl.sub.3 containing up to
about 34 weight % AlCl.sub.3 ;
(b) combining the AlCl.sub.3 solution with an aqueous solution of
citric acid containing up to about 50 weight % citric acid, while
vigorously agitating the resultant solution to form an aluminum
citrate solution having a mole ratio of aluminum ion to citric acid
molecule of from about 1.5:1 to about 2:1, said AlCl.sub.3 solution
being provided in an amount sufficient to form an aluminum citrate
solution containing from 1 up to about 3 weight % aluminum; and
(c) adding a basic hydroxide of the formula MOH where M is an
alkali metal or ammonium cation to the aluminum citrate solution,
while continuing to vigorously agitate the solution and while
maintaining its temperature within the range of from 20.degree. C.
to 90.degree. C., in sufficient quantity to raise the pH of the
solution to a level of from 5.5 to 7.5.
DESCRIPTION OF THE INVENTION
The present invention provides the following advantages over the
prior art method of dissolving a dry blend of aluminum sulfate and
sodium citrate in water at the well site:
1. There are no solids in the solution to cause wear and tear on
pumping equipment.
2. The aluminum citrate liquid can be shipped from the formulation
site to the well site in tank trucks, stored in bulk and pumped
into the formation when desired.
3. There is afforded complete control over the pH of the solution
resulting in low corrosion rates and optimum gelling
performance.
4. There is no manual handling of dry material required which
results in a safer operation.
5. There is no opportunity for operator error since the product is
complete as it arrives at the well site.
In each of the process steps, there have been discovered certain
critical parameters which are necessary to the successful formation
of a stable solution.
In a typical formulation, sufficient aluminum chloride is used to
provide a mole ratio of aluminum to citric acid molecule of from
about 1.5:1 to about 2:1. At higher ratios of aluminum ion to
citric acid molecule, the solids will precipitate from solution at
a pH level in the range suitable for use in enhanced oil recovery
resulting in a drastically reduced amount of aluminum being made
available to cross-link the polymer in the oil bearing formation.
At a ratio below about 1.5:1, the time required to cross-link the
polymer, as determined by the gelling rate, is unacceptably long.
For maximum stability of the solution, a ratio of about 1.9:1 has
been found to be preferable.
Aluminum chloride solutions containing up to about 34 weight % salt
are commercially available. Since more concentrated solutions are
not stable, this is the maximum practical concentration. Less
concentrated solutions are suitable, but since it is desirable to
provide an aluminum citrate solution which is highly concentrated
yet stable, a concentrated (32.degree. Be) solution is preferred.
Likewise, it is desirable to use a citric acid solution which
contains up to about 50 weight % citric acid, although less
concentrated solutions can be employed. For economic reasons, it is
desirable to provide an aluminum citrate solution having as high a
concentration of aluminum as possible. A solution containing less
than 1 weight % aluminum would be impractical because of the larger
volume of solution which would be required to provide the needed
amount of aluminum to the oil bearing formation. It has been
discovered that the process of the present invention can be used to
provide an aluminum citrate solution containing up to about 3
weight % aluminum. When mixing the aluminum chloride and citric
acid solutions, it is essential that vigorous agitation be
maintained throughout the process until a clear solution of
aluminum citrate is achieved. At this point, the solution's pH is
too low for compatibility with its use in the above-described
enhanced oil recovery techniques because of the solution's tendency
to be corrosive. Furthermore, the aluminum citrate is not very
soluble at a lower pH in the ratio of aluminum ion to citric acid
molecule desirable for enhanced oil recovery. The addition of an
alkali metal or ammonium hydroxide is necessary to raise the pH to
the desired level. This is accomplished by adding an aqueous
solution of the basic material to the aluminum citrate solution in
sufficient quantity to raise its pH to a level of from 5.5 to 7.5,
preferably from 6.0 to 7.0. Alternatively, ammonia gas can be
bubbled into the solution to form ammonium hydroxide in situ. When
dry ammonia is used as the source of the base, some dilution of the
aluminum citrate solution is desirable to avoid precipitation.
Vigorous agitation of the solution is essential during the addition
of the base to prevent precipitation of the aluminum already in
solution in the form of aluminum hydroxide which will reduce the
aluminum assay of the solution. In addition, temperature control is
essential during this step due to the exothermic reaction which
results upon addition of the base. The temperature should be
maintained within the range of from 20.degree. C. to 90.degree. C.
during this step with a temperature in the range of from 40.degree.
C. to 60.degree. C. being preferred. Slow addition of the base
together with external cooling have been found adequate to maintain
the temperature within the desired range.
An aluminum citrate solution prepared in the above-described manner
will remain stable for a period of from 10 to 14 days. It has been
discovered that the period of stability can be increased by adding
sufficient base to raise the pH to a level of 6.0 to 7.0 and then
lowering the pH to a level of from 5.0 to 5.5 by the addition of a
mineral acid, preferably HCl. However, in this embodiment, it is
necessary to increase the pH from 5.0 to at least 5.5 before
injecting the solution into the formation in order to achieve
optimum results in the tertiary oil recovery procedure.
The method of practicing the present invention is further
illustrated by the following examples:
EXAMPLE I
A 600 ml beaker was charged with 258 g of a commercially available
34 weight % AlCl.sub.3 solution and 107.65 g of a 50% citric acid
solution to provide a mole ratio of aluminum to citric acid of 2:1.
The resulting solution was stirred vigorously for 35 minutes after
which period 25 ml of a 50% NaOH solution was added via burette
over a period of 36 minutes.
This procedure resulted in a liquid aluminum citrate having the
following specifications:
______________________________________ Aluminum Assay = 2.9% w/w
(3.7% w/v) pH = 6.8 Sq. Gravity = 1.295 Freezing = -20.degree. C.
(crystallization point) ______________________________________
This solution remained stable for a period of approximately 2
weeks.
EXAMPLE II
The following experiment was run to develop a formulation based on
2.0 moles of Al to 1.1 mole of citric acid:
A 250 ml beaker was charged with 55 g of a 34% solution of aluminum
chloride. To this was quickly added 25.3 g of a 50% (w/w) citric
acid solution and 30.0 g of a 50% NaOH solution was added, while
keeping the temperature at about 60.degree. C., to bring the pH to
6.5. This procedure provided a crystal clear solution having a
specific gravity of 1.293 which remained stable for approximately 2
weeks.
EXAMPLE III
The following procedure was carried out in a 21,196 liter
fiberglass mix tank equipped with 10 coils of a 3.8 cm diameter
polyvinyl chloride cooling coil, a turbine agitator and 1 air wand
for additional agitation.
The procedure was as follows:
______________________________________ Day 1
______________________________________ 4:30 p.m. The tank was
charged with 7,986 liters of a 34% aluminum chloride solution
directly from a tank truck. 7:30 p.m. Citric acid, 3.857 liters of
a 50% (w/w) solution, was added while maintaining vigorous
agitation. 9:00 p.m. Slow addition of a 50% (w/w) NaOH solution was
commenced with external cooling of the vat. At this point, the pH
was less than 1 and the temperature was 55.degree. C. Addition of
the sodium hydroxide was con- tinued for approximately 18 hours
under the following schedule:
______________________________________ Day 2 Temperature pH
______________________________________ 7:30 a.m. 55.degree. C. --
4:00 p.m. 53.degree. C. 1.24 8:30 p.m. 54.degree. C. 2.76 12:00
midnight 54.degree. C. 4.72 ______________________________________
Day 3 Temperature pH ______________________________________ 12:18
a.m. 54.degree. C. 5.39 12:44 a.m 55.degree. C. 6.05 1:01 a.m.
55.degree. C. 6.20 1.15 a.m. 55.degree. C. 6.40 1:30 a.m. -- 6.57
______________________________________
By the time the desired pH was achieved, the total amount of NaOH
added was 3,709 liters. This procedure provided 15,140 liters of
liquid aluminum citrate containing 2.97% (w/w) aluminum.
After 2 weeks, a sample of the material became cloudy. Analysis of
the clear supernatant showed 2.74% (w/w) aluminum indicating that
7.7% of the original aluminum had precipitated out.
EXAMPLE IV
A 600 ml beaker was charged with 169.6 g of AlCl.sub.3 (32.degree.
C.-11.03 g Al) or 0.409 mole. To this was added 82.6 g of 50%
citric acid (41.3 g citric acid/0.215 mole). With agitation, the
resultant was slowly neutralized to the pH level shown in the
following table by adding 50% NaOH dropwise while keeping the
temperature between 40.degree. C. and 55.degree. C. At each pH
value, the volume of precipitate and the amount of aluminum in
solution, as determined by atomic absorption assay, were recorded.
This material exhibited the following solubility at the various pH
levels:
______________________________________ Al in Volume pH Solution of
Ppt. ______________________________________ 5.5 35,000 ppm 0% 6.0
33,000 0 6.5 34,000 0 7.0 33,000 0
______________________________________
Following the procedure of British Patent Specification No.
1,598,709, a 250 ml beaker was charged with 5.12 g of anhydrous
citric acid (0.27 mole) and 22.48 g of distilled water with
stirring until the citric acid had dissolved. To this was added 33
g of AlCl.sub.3 solution (32.degree. C. Be) and 33 g of an Al.sub.2
(SO.sub.4).sub.3 solution containing 17% Al.sub.2 O.sub.3 which was
then stirred for 5 minutes. This provided a total of 0.141 mole of
aluminum ion. At this point, there was added 10 g of concentrated
H.sub.2 SO.sub.4 and 32 g of distilled water and the resultant was
neutralized slowly to a pH of 4.0 by the addition of 83.5 ml of 20%
NaOH with agitation while maintaining the temperature of the
solution below 35.degree. C. The amount of aluminum in solution and
volume of precipitate was determined at each 0.5 pH unit as the pH
was increased from 4.0 to 7.0 with the results being reported in
the following table:
______________________________________ Al in Volume pH Solution of
Ppt. ______________________________________ 4.0 16,800 ppm 0% 4.5
14,800 16 5.0 13,600 23 5.5 1,200 94 6.0 800 93 6.5 500 100 7.0 400
89 ______________________________________
The prior art method calls for stopping the neutralization of the
aluminum citrate solution at pH 4.2 at which point the solution is
clear. This pH, however, is too low for the proper cross-linking of
polymers and results in a weak, unstable gel. Raising the pH to the
range of 5.5 to 7.5 causes the aluminum to precipitate out
rendering the material unsuitable for the intended purpose.
EXAMPLE V
A performance test for determining the ability of aluminum citrate
to cross-link polymers which has been accepted by many major oil
producing concerns is conducted as follows:
Procedure
1. Acidify 100 ml of carboxymethyl cellulose (CMC) solution (5,000
ppm CMC in 1% KCl solution) in a 250 ml beaker to pH 3.5 using 15%
HCl.
2. Add 3.3 ml.+-.3% Al of aluminum citrate solution using more than
3.3 ml if concentration of Al is less than 3%.
3. Stir until homogeneous. The pH of the combination of the polymer
and aluminum citrate solution is about pH 4.5. This pH is lower
than one would prefer to encounter in an oil bearing formation
because it results in too rapid gel formation. However, a low pH
and consequent rapid gel formation has been found to be desirable
for this accelerated test.
4. Pour into ca. 1 inch diameter glass test tube.
5. Record firm gel time as no air bubble rising when inverting test
tube.
6. Acceptable material gels in less than 30 minutes. Most will gel
in less than 15 minutes.
Using this procedure, the gelling times for aluminum citrate
solutions having ratios of aluminum ion to citric acid molecule of
from 1.0:1.0 to 2.0:1.0 were obtained. The results of this
experiment are set out in the following table:
______________________________________ Al to Citrate Molar Ratio
Gel Test Time ______________________________________ 2.0 Al:1.0
Citrate 1 minute 1.9:1.0 1 1.8:1.0 2 1.7:1.0 5 1.6:1.0 17 1.5:1.0
12 1.4:1.0 3 hours 1.3:1.0 16 1.2:1.0 No gel in 3 days 1.1:1.0 No
gel in 3 days 1.0:1.0 No gel in 3 days
______________________________________
From the above data, it can be determined that an aluminum citrate
solution with a mole ratio of aluminum ion to citric acid molecule
of at least about 1.5:1 is necessary for the satisfactory
cross-linking of carboxymethylcellulose which is a preferred
cross-linkable polymer for use in enhanced oil recovery.
* * * * *